Heretofore, titanium catalysts composed of titanium compounds and organoaluminum compounds or vanadium catalysts composed of vanadium compounds and organoaluminum compounds have been known as catalysts for use in preparing .alpha.-olefin polymers, for example, ethylene polymers or ethylene/.alpha.-olefin copolymers.
Generally speaking, ethylene/.alpha.-olefin copolymers obtained by using titanium catalysts involved such problems that they are found to have relatively broad molecular weight distribution and compositional distribution and, moreover, are found to be relatively poor in transparency, surface tackiness and dynamic physical properties. Furthermore, ethylene/.alpha.-olefin copolymers obtained by using vanadium catalysts were found to be low in polymerization activity and required to adopt deashing operation, though they were found to be narrower in molecular weight distribution and compositional distribution and, moreover, they were improved fairly in transparency, surface tackiness and dynamic physical properties in comparison with ethylene/.alpha.-olefin copolymers obtained by using titanium catalysts. Accordingly, the advent of catalyst systems having been further improved in these properties as mentioned above has been desired.
On the one hand, there have been proposed recently processes for preparing ethylene/.alpha.-olefin copolymers using catalysts composed of zirconium compounds and aluminoxane as novel Ziegler-type catalysts.
For instance, Japanese Patent L-O-P Publn. No. 19309/1983 discloses a process for preparing ethylene/.alpha.-olefin copolymers by polymerizing ethylene and one or two or more C.sub.3 -C.sub.12 .alpha.-olefins at a temperature of from -50.degree. C. to 200.degree. C. in the presence of a catalyst composed of a transition metal containing compound represented by the following formula EQU (Cyclopentadienyl).sub.2 MeRHal
wherein R is cyclopentadienyl, C.sub.1 -C.sub.6 alkyl or halogen, Me is a transition metal and Hal is halogen, and a linear aluminoxane represented by the following formula EQU Al.sub.2 OR.sub.4 (Al(R)-O).sub.n
wherein R is methyl or ethyl and n is a number of from 4 to 20, or a cyclic aluminoxane represented by the following formula ##STR1## wherein R and n are as defined above. This publication cited above teaches that the polymerization of ethylene should be carried out in the presence of a small amount such as up to 10% by weight of somewhat long chain .alpha.-olefin or mixture thereof in order to regulate a density of the resulting polyethylene.
Japanese Patent L-O-P Publn. No. 95292/1984 discloses an invention relating processes for preparing linear aluminoxanes represented by the following formula ##STR2## wherein n is 2-40, and R is C.sub.1 -C.sub.6 alkyl, and cyclic aluminoxanes represented by the following formula ##STR3## wherein n and R are as defined above. The publication as cited above discloses that at least twenty-five million grams per 1 g of a transition metal and per 1 hour of polyethylene are obtained by carrying out olefin polymerization in the presence of a mixture obtained by the process of said publication, for example, by mixing methylaluminoxane with a bis(cyclopentadienyl) compound of titanium or zirconium.
Japanese Patent L-O-P Publn. No. 35005/1985 discloses a process for preparing polymerization catalysts for olefin which comprises first reacting an aluminoxane compound represented by the following formula ##STR4## wherein R.sup.1 is C.sub.1 -C.sub.10 alkyl, and R.sup.0 is R.sup.1 or represents --O-- by linkage, with a magnesium compound, then chlorinating the resulting reaction product, followed by treatment with Ti, V, Zr or Cr compound. This publication as cited above discloses that the above-mentioned catalysts are particularly useful for copolymerization of mixtures of ethylene and C.sub.3 -C.sub.12 olefins.
Japanese Patent L-O-P Publn. No. 35006/1985 discloses combinations of mono-, di- or tri-cyclopentadienyl or derivatives thereof and at least two kinds of transition metals (a) and aluminoxane (b) as catalyst systems for use in preparation of reactor blend polymers. Example 1 of the above-cited publication discloses polyethylene having a number average molecular weight of 15,300, a weight average molecular weight of 36,400 and containing 3.4% of propylene component, said polyethylene being obtained by polymerization of ethylene and propylene in the presence of a catalyst composed of bis(pentamethylcyclopentadienyl)zirconium dimethyl and aluminoxane. Further, Example 2 of this publication discloses a blend of polyethylene and ethylene/propylene copolymer having a number average molecular weight of 2,000 and a weight average molecular weight of 8,300 and containing 7.1 mol % of propylene component, which is obtained by polymerization of ethylene and propylene in the presence of a catalyst composed of bis(pentamethylcyclopentadienyl)zirconium dichloride, bis(methylcyclopentadienyl)zirconium dichloride and aluminoxane, said blend comprising a toluene-soluble moiety having a number average molecular weight of 2,200 and a weight average molecular weight of 11,900 and containing 30 mol % of propylene component and a toluene-insoluble moiety having a number average molecular weight of 3,000 and a weight average molecular weight of 7,400 and containing 4.8 mol % of propylene component. Example 3 of this publication further discloses a blend of LLDPE and ethylene/propylene copolymer, which is obtained in the manner similar to that of Example 2 mentioned above, said blend comprising a soluble moiety having a molecular weight distribution (Mw/Mn) of 4.57 and containing 20.6 mol % of propylene component and an insoluble moiety having a molecular weight distribution of 3.04 and containing 2.9 mol % of propylene component.
Japanese Patent L-O-P Publn. No. 35007/1985 discloses a process for polymerizing ethylene alone or ethylene and .alpha.-olefin of at least 3 carbon atoms in the presence of a catalyst system containing metallocene and a cyclic aluminoxane represented by the following formula ##STR5## wherein R is alkyl of 1-5 carbon atoms and n is an integer of 1 to about 20, or a linear aluminoxane represented by the following formula EQU R(R-Al-O).sub.n AlR.sub.2
wherein R and n are as defined above. According to the disclosure of the publication cited above, the polymers obtained in the process have weight average molecular weight of about five hundred to about fourteen million and a molecular weight distribution of 1.5-4.0.
Japanese Patent L-O-P Publn. No. 35008/1985 discloses polyethylene or copolymers of ethylene and C.sub.3 -C.sub.10 .alpha.-olefin having a broad molecular distribution which are prepared by using a catalyst system containing at least two kinds of metallocenes and aluminoxane. The copolymers obtained in this manner are alleged to have a molecular weight distribution (Mw/Mn) of 2-50.
In Japanese Patent L-O-P Publn. Nos. 260602/1985 and 130604/1985, there are proposed processes for polymerizing olefins in the presence of catalysts formed from mixed organoaluminum compounds comprising aluminoxanes and organoaluminum compounds, and these publications disclose that by virtue of the addition of the organoaluminum compounds, the polymerization activity per unit transition metal improves.
Japanese Patent L-O-P Publn. No. 36390/1987 teaches that aluminoxanes are obtained by reaction of organoaluminum compounds with iron compounds containing water of crystallization, Japanese Patent L-O-P Publn. No. 148491/1987 teaches that aluminoxanes may be obtained by reaction of organoaluminum compounds with compounds containing water of crystallization selected from the group consisting of magnesium compounds, nickel compounds and lanthanide compounds, and Japanese Patent L-O-P Publn. Nos. 56507/1988 and 56508/1988 teach that aluminoxanes can be obtained by reaction of water directly with organoaluminum compounds in inert hydrocarbon solvents utilizing a high speed, high shearing ability induction type impeller or an ultrasonic wave.
In preparing .alpha.-olefin (co)polymers in the manner now described, when the aluminoxane compounds are used as one component of the catalyst therefor, .alpha.-olefin (co)polymers having a narrow molecular weight distribution and a narrow compositional distribution can be obtained with excellent polymerization activity.
However, a great desideratum for the industry concerned is the advent of such aluminoxane type organoaluminum compounds as having excellent polymerization activity on .alpha.-olefin and as being capable of giving olefin (co)polymers having a narrow molecular weight distribution and a narrow compositional distribution.
In this connection, known aluminoxane compounds used hitherto in olefin polymerization, even when they are used in a state of liquid or solid, were prepared and recovered as those which are soluble in hydrocarbon solvents such as benzene or toluene, and their molecular weight was determined by cryoscopic method after dissolving them in benzene and, moreover, a structure of said aluminoxane was decided by measuring a freezing point thereof in benzene.
In light of the foregoing points, the present inventors prosecuted extensive researches and eventually have accomplished the present invention on the basis of their finding that novel organoaluminum oxy-compounds which have not been known at all hitherto and which are insoluble or sparingly soluble in benzene and toluene exhibit excellent catalytic activities in olefin polymerization. The phrase "benzene-insoluble" is used herein to refer to the organoaluminum oxy-compounds of the present invention which are insoluble or only sparingly soluble in benzene and, which are characterized by less than 10% solubility in terms of Al atom in hydrocarbon solvents such as benzene.